N55 crankhub and timing guide
Factory torque specs, special tools, and honest job sequences for the N55 crankhub, vibration damper, timing chain, and VANOS gear bolts — from ISTA.
The N55 inherits the N54's crankhub architecture — damper ring, hub, single central bolt, friction drive to the chain sprocket — with one bigger bolt and its own chain-drive revisions mid-production. The factory data splits the timing chain job at March 2012, and carries a dedicated procedure for the aluminium VANOS gear screws that is pure gold if you have the cylinder head cover off. All of it below, traced to ISTA document ids.
The crankhub, factory view
Damper-off (11 23 010) is deliberately shallow: eight screws out, damper off, and the hub stays put. ISTA states the law in one line — do not release the central bolt — and the consequence: if it is accidentally loosened, the timing must be readjusted. The damper job's only real decisions are how you hold the crank:
- Gearbox removed: block the crankshaft with `11 9 260`
- Manual gearbox installed: `11 8 180`
- Automatic installed: `11 8 660`
When the central bolt does have to come out (timing chain job), it is a bigger fastener than the N54's and a different angle:
Crankhub torque table
| Fastener | Thread | Spec | Torque |
|---|---|---|---|
| Hub (torsion damper) to crankshaft, central bolt 12.9 | M18 x 108 | Replace. Lightly oil screw and thread | 100 Nm (73.8 lb-ft) + 270° |
| Vibration damper to crankshaft hub, screws 10.9 | M8 x 16 | — | 35 Nm (25.8 lb-ft) |
Timing chain, guides, and tensioner
ISTA carries two versions of the chain job, split at March 2012 production. The procedure difference is in how you make the chain safe before touching the central bolt:
- **Up to March 2012:** relieve the chain tensioner, press the chain with tensioner in the direction of travel, and disconnect the chain with tool `11 4 120`.
- **From March 2012:** the hydraulic chain tensioner must be drained first — press the tensioning rail with a suitable screwdriver, repeatedly, because the oil pressure only drains pulsating. Then press and hold the rail and lock the tensioner piston with a suitable lock pin. The oil-pump chain tensioner sealing cap also comes off as a preliminary task on these engines.
That production split is a factory-documented design change — it is the honest version of the "which chain do I have" question. Your build date decides which procedure applies.
Chain drive torques
| Fastener | Thread | Torque |
|---|---|---|
| Chain drive module to cylinder head | M6 x 35 | 8 Nm (5.9 lb-ft) |
| Guide rail to crankcase | M8 | 20 Nm (14.8 lb-ft) |
| Guide rail to cylinder head | M7 | 14 Nm (10.3 lb-ft) |
| Chain tensioner to cylinder head | M22 x 1.5 | 55 Nm (40.6 lb-ft) |
| Screw plug in cylinder head | M18 x 1.5 | 25 Nm (18.4 lb-ft) |
| Eccentric shaft bearing cap to cylinder head | M6 x 27 | 8.5 Nm (6.3 lb-ft) |
| Camshaft bearing cap to cylinder head | M6 x 30.5 | 8.5 Nm (6.3 lb-ft) |
| Camshaft bearing strips (steel screw 10.9) | M7 x 70 | 8 Nm (5.9 lb-ft) + 60°, inserted dry |
The tensioner on its own (11 31 090) is one of the cheapest meaningful jobs on this engine: air duct off, tensioner out, new sealing ring, 55 Nm.
VANOS gear screws — the aluminium-bolt procedure
The N55 has a dedicated factory procedure for the VANOS gear screw connection, and it exists because these are aluminium screws with their own laws:
- Replace every aluminium screw each time it is released. No exceptions in the document.
- Jointing torque and angle must be observed without fail — risk of damage.
- Maximum permissible temperature difference between screw and VANOS gear: **20°C**. Ideal conditions mean identical temperatures.
- Torque: **6 Nm (4.4 lb-ft) + 65°**, set on special tool `2 333 991` or `0 418 185`.
- Tighten crosswise in sequence 1 to 4, rotating the engine 360° at the central bolt between positions, and mark every replaced screw with a colour mark.
- Clean the thread with brake cleaner and blow it out thoroughly before the new screw goes in.
VANOS adjuster central bolts
| Fastener | Thread | Spec | Torque |
|---|---|---|---|
| VANOS with sensor wheel to inlet and exhaust camshafts | M10 x 94 | Replace screw | 20 Nm (14.8 lb-ft) + 180° |
| Non-return valve VANOS to cylinder head | M14 x 1.5 | — | 13 Nm (9.6 lb-ft) |
Special tools
- `11 9 260` / `11 8 180` / `11 8 660` — crankshaft blocking (engine out / manual / automatic)
- `11 4 120` — chain disconnect (pre-March 2012 chain job)
- `11 0 300` — TDC locking pin
- `11 4 280` / `11 4 281` / `11 4 283` — flywheel counterhold and camshaft locking fixtures
- `2 333 991` or `0 418 185` — torque-angle tool for the aluminium VANOS screws
- `11 9 340` + `00 9 250` — chain pre-tension (0.6 Nm) for timing adjust
Coverage notes
The data carries complete damper, chain, tensioner, and VANOS-gear procedures with the March 2012 split, all torques above. It does not publish failure-mileage statistics for the chain or hub — nothing in the factory docs supports a "fails at X miles" claim, so we won't make one. The 2012 production change and the aluminium-screw procedure are the factory's own paper trail of the N55 chain drive evolving; if you're buying parts for a chain job, the build date is the first thing to check.
Every number traces to the ISTA ids in the sources; the full procedures live in ISTA.
- 11 23 010 — Removing and installing/replacing vibration damper (N55)
- 11 31 051 — Replacing timing chain (N55) up to March 2012
- 11 31 051 — Replacing timing chain (N55) from March 2012
- 11 31 090 — Installing and removing/replacing chain tensioner piston (N55)
- 11 36 ... — Replacing screw connection on VANOS gear (N55)
- 11 21 1AZ — Torsion damper (hub) to crankshaft, central bolt (N55)
- 11 23 1AZ — Vibration damper to crankshaft hub screws (N55)
- 11 31 2–8AZ — Chain drive module, rails, chain tensioner, caps (N55)
- 11 36 1AZ — VANOS with sensor wheel to inlet and exhaust camshafts (N55)